Thermoplastic polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), are well known engineering resins and are used extensively to form a variety of molded articles due to their favorable mechanical, physical and chemical properties. Thus, molded articles formed of polyester resins have been employed as component parts for automobiles, electric and electronic apparatus, tools, and precision machines.
Recently, there has been a need to reduce the weight of many apparatus and machines which include components formed of molded polyester resins. For example, the weight of automobiles has been desired as one means to reduce fuel consumption. Furthermore, in the electric and electronics appliance industries, weight reduction is a desirable objection so as to facilitate greater ease of handling of the apparatus as a whole (e.g., so as to make the apparatus more easily transported by the consumer).
Attempts have been made to reduce the weight of apparatus generally by using lighter weight (lower specific gravity) component parts without sacrificing the functions and/or properties that are needed. A possible technique for reducing the weight of molded parts formed of thermoplastic polyester resin involves incorporating into the polyester base resin, a polyolefin resin having a lesser specific gravity. However, since polyester and polyolefin resins form an incompatible blend, surface peeling is often observed on molded articles due to insufficient dispersion of the polyolefin throughout the polyester base resin thereby deleteriously affecting the articles' impact strength. As a practical matter, therefore, a commercially viable polyester molding composition cannot be obtained simply by melt-blending a polyolefin resin with a polyester base resin.
There have, however, been attempts to improve the incompatibility of polyester and polyolefin resins, as disclosed, for example, in Japanese Patent Publication Nos. 60744/1986 and 60756/1986. In the former, a technique is disclosed whereby a copolymer of an epoxidized ethylene or ethylenically unsaturated compound is used as a compatibilizing agent. In the latter, a technique is disclosed whereby a modified polypropylene is used in addition to the copolymer of an epoxidized ethylene or ethylenically unsaturated compound so as to improve compatibility with polyester resins.
Notwithstanding these prior proposals, there still exists a need for improved and compatible blends of polyester and polyolefin resins so that more lightweight polyester resin compositions, and molded parts thereof, may be produced. It is towards fulfilling such a need that the present invention is directed.
Broadly, the present invention principally resides in the discovery that the compatibility of thermoplastic polyester and polyolefin resins can be significantly improved by incorporating a compatibilizing compound having both a carbon-carbon double bond and an epoxy group in its molecule, and by melt-blending the components in the presence of a radial initiator.
More specifically, the present invention relates to a moldable thermoplastic polyester resin composition which includes:
(A) between 97 to 20 parts by weight (based on 100 parts by weight of the compositions) of a polyester base resin; PA1 (B) between 3 to 80 parts by weight (based on 100 parts by weight of the composition) of a polyolefin resin; PA1 (C) between 0.1 to 15 parts by weight (based on 100 parts by weight of the composition) of a compatibilizing compound having both a carbon-carbon double bond and an epoxy group in its molecular structure; and PA1 (D) between 0.1 to 20 % by weight of the compatibilizing compound, of a free radical initiator.
These components are preferably melt-blended in the presence of the free radical initiator for a time period of at least 30 seconds. Optionally, the compositions of this invention may further be blended with (E) up to 120 parts by weight (based on 100 parts by weight of the composition) of at least one filler material (in the form of solid or hollow fibers, powders, flakes or the like).
Further aspects and advantages of this invention will become more clear after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follows.